问题 Code scattering Blocks of duplicated code Blocks of complementary code, and different modules implementing complementary parts of the concern Code tangling Code tangling occurs when a module has to manage several concerns at the same time such as logging, exception handling, security, caching, and more or when a module has elements of the implementation of other concerns inside.

AOP 面向对象 Aspect Class Joinpoint This is the application point of the aspect. It is a point of the execution of a program such as the invocation of a constructor or the execution of a method or the management of an exception (WHEN). Advice This is the action an aspect performs at a certain joinpoint. Advices can be "around", "before", and "after". Pointcut This is the expression for the joinpoint's selection, for instance a method's execution with a certain signature (WHERE)

AOP 面向对象 Introduction This is the declaration of methods or additional fields on the object to which the aspect will be applied. It allows the introduction of new interfaces and implementations on the objects. Target object This is the module (Object) to which the aspect will be applied. Weaving This is the linking action between the aspect and the objects to which advices must be applied

AOP 面向对象 Before advice After returning advice Throws advice After (finally) advice Around advice

the crosscutting concerns should be analysed as a third dimension of the design. In these situations, aspect-oriented programming provides support to object-oriented programming for uncoupling modules that implement crosscutting concerns.

 Spring XML 方式  AspectJ annotation 方式  Schema-based 配置方式

Spring permits only method execution to be used as a joinpoint. So we can't use with Spring AOP all the features of AOP, but we can do so with AspectJcalled by Spring. For example, we must use the support of AspectJif we want to use as a joinpoint:  The invocations of constructors  Access to the domains of objects with the setter and getter  The initialization of an object  The initialization of an object with a calling super()  The execution inside a class with this()  The calling of a method

 A pointcut is an expression for the selection of joinpoints. It can be a collection of joinpoints used to define an advice that has to be executed. Methods starting with a certain prefix (such as, getter and setter) Methods with a particular package (such as org.springaop.domain.*) Methods that return a certain kind of output (such as public MyClass get*(...)) A pointcut is the composition of a ClassFilter and a MethodMatcher.

 1. NameMatchMethodPointcut  2. RegexpMethodPointcut  3. StaticMethodMatcherPointcut  4. DynamicMethodMatcherPointcut  ComposablePointcut  ControlFlowPointcut

 public class NameMethodMatcherExample {  public static void main(String[] args) {  NameMethodTargetExample target = new NameMethodTargetExample();  NameMatchMethodPointcut pc = new NameMatchMethodPointcut();  pc.addMethodName("printSpot");  pc.addMethodName("printAction");  Advisor advisor = new DefaultPointcutAdvisor(pc, new AdviceExample());  ProxyFactory pf = new ProxyFactory();  pf.setTarget(target);  pf.addAdvisor(advisor);  NameMethodTargetExample proxy = (NameMethodTargetExample)pf.getProxy();  proxy.printName();  proxy.printAction();  proxy.printSpot();  }

 A joinpoint is a well-defined point during the execution of your application. Typical examples of joinpoints include a method call, method execution, class initialization, and object instantiation. Joinpoints are a core concept of AOP and define the points in your application at which you can insert additional logic using AOP.  Spring AOP only supports one joinpoint type— method invocation.

 An advice specifies what must be done at a joinpoint.  Spring uses a chain of interceptors to wrap the invocation of the method and apply to it the advices contained into this chain. As said before, Spring is consistent with the specifications of the AOP Alliance, but provides a slightly different programming model

 Before Advice  After Returning Advice  After throwing Advice

 The advisor isn't a concept from AOP in general, but is specific to Spring AOP.  The advisor links together pointcuts and advice. So it contains both the action to be executed (defined in the advice) and the point where it is to be executed (defined in the pointcut). The advisor's role is to decouple pointcuts and advice, in order to reuse them independently from each other.

 Introductions are a very strong component of the Spring AOP. They permit us to dynamically introduce new one-object functionalities as the implementation of interfaces on existing objects:  To create a mixin, adding to the state held in the object. This is probably the most important use.  To expose additional states associated with a special TargetSource. This is used within Spring, for example, with scripting support.  To expose an object or object graph in a different way—for example, making an object graph implement the XML DOM interfaces.

 a normal advice can be applied to any object since it has a per-class lifecycle,  an introduction has a per-instance lifecycle.

This allows us to focus our attention and development on crosscutting concerns to apply through the proxy, rather than focus on the proxy. setTarget: Specify the target object you want to proxy. setProxyTargetClass: The default behavior is the following:  If an interface is available, it's used as a JDK proxy.  If an interface is not available, it's used as a CGLIB proxy.  If we set the value to true, it's used as a CGLIB proxy.

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